1. Field of the Invention
The present invention relates to a heating device that produces heat by making use of induction heating, and a fixing unit in which the heating device is mounted.
2. Description of the Related Art
A heating device using induction heating is employed in a fixing device that is mounted in an electrophotographic copying machine.
As is disclosed in, for instance, Jpn. Pat. Appln. KOKAI Publication No. 9-258586, in this kind of heating method, eddy current is caused in a fixing (heating) roller, using a coil that is wound around a core extending along the rotational axis of the roller. Thus, the roller is heated.
Jpn. Pat. Appln. KOKAI Publication No. 8-76620 discloses a heating device wherein magnetic field generating means applies a magnetic field to a heating belt so that the heating belt produces heat by induction heating. The heating belt is clamped between a pressing belt and the field generating means, thus forming a nip.
In this type of heating device using induction heating, radio frequency (RF) power is supplied to the excitation coil, thereby to quickly raise the temperature up to a level that is needed for fixation. As a result, resonance noise is produced due to resonance of the excitation coil.
Consequently, there arises such a problem that a holder member that holds the excitation coil, or a coil unit that includes a magnetic core for enhancing magnetic flux may be damaged.